Everyone claims to desire to be happy, but that is so momentary, and what most people call happiness vanishes when the ride is over. Tranquility is a more desirable emotional condition because it is just as pleasant and can be held for a longer time. Each of these two conditions is dependent on something desirable being enjoyed in the moment.
Tranquility is more under conscious control; at least it can be controlled by people who are in a mature frame of mind, because when in that state they can choose to be tranquil. They can look at reality clearly, to participate in the world around them at their discretion. With that level of self-control they can choose to be in nearly any emotional state they desire, and as tranquility is pleasant, and also pleasant for the people around them, it is a desirable emotion to choose.
One of the chief characteristics of a person capable of tranquility is a clear understanding of their limitations. As a person inhabiting this moment in time and this place in space, they are not responsible for the many problems of the world. The media sprays a constant mist of fear and lack of control upon the public, but a person who realizes they have no control over these events, and thus no responsibility, need not give those events anything more than cursory attention. The advantage of this form of ignorance is that the worries associated with those kinds of public problems vanish, and it becomes easier to be tranquil. I can be comfortable with the functioning of the Universe, and let it take care of itself.
There are horrible things that can and will happen in the world, and eventually we ourselves will die. That is inevitable, and being inevitable it can be accepted as outside of one’s control, and being of that category of things one can’t do anything about, it may be safely ignored. Once that reality is accepted, which is easy once you realize it is inevitable, then you can go back to a comfortable state of tranquility. Even the horrible things that happen can be accepted because of the remoteness of their occurrence, and we can put our energies into being as kind as possible to the people we encounter. Of course we can participate as much as other people in easing the problems of the world, but once you become aware of the level of input that is expected of you and give that amount, you can relax and go back into your tranquil frame of mind.
The way we influence things is by controlling the precursors to events, but responding to problems after they become obvious to the public and the media will leave you as stressed as they are. With a little foresight about the way things are trending, it is usually easy to pre-adapt to the coming problems. In addition to foresight, that pre-adaptation requires a little buffer, sometimes called slack, so you can make the needed adjustments early when it is easy and cheap.
Tranquility is as easy as creating habits to see and react properly to the precursors.